4 ms·

I'm looking at http://www.ars.usda.gov/Services/docs.htm?docid=18349 http://www.ars.usda.gov/Services/docs.htm?docid=18349 (2001-2012) and http://www.ars.usd

I'm looking at http://www.ars.usda.gov/Services/docs.htm?docid=18349 http://www.ars.usda.gov/Services/docs.htm?docid=18349 (2001-2012) and http://www.ars.usda.gov/Services/docs.htm?docid=14392 http://www.ars.usda.gov/Services/docs.htm?docid=14392 (1935-1998) I'm really suspicious that such a large jump happens to coincide with "new" vs. "old" surveys, and indeed the pre-2000 page says: CHANGES IN METHODS AND OPERATIONS ACROSS SURVEYS… It is important to consider that survey methods and operations including questionnaire wording, data processing methods, and the survey nutrient database used to calculate the dietary intake were changed from survey to survey based on new data and methods available at the time. Comparing data across surveys must take into account these types of changes. Does anyone think CSPI really spent the time digging into this anomaly that they would have if it had been purported "good news"? Did they spend any time digging in at all? Who knows... which is why, as I said, I don't take their chart very seriously.

deleted 11y ago
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zzalpha 11y ago
That's actually a very good observation! There does seem to be a major discontinuity between those two study periods. Very strange that it seems to only affect fats, and that the effect was so dramatic... They do mention "There has been some research that addressed the impact of changes in methods and/or databases between selected surveys"... it'd be worth digging that up to see what the effects were determined to be. Edit: Found it? http://naldc.nal.usda.gov/catalog/7349 http://naldc.nal.usda.gov/catalog/7349 Nothing in the abstract explains a major discontinuity in reported fat intake, though. They only report small but statistically significant effects on various other nutrients. Edit 2: They also have a FAQ on this topic. From http://www.ars.usda.gov/Services/docs.htm?docid=13793 http://www.ars.usda.gov/Services/docs.htm?docid=13793: "Is it possible to combine WWEIA data from different release cycles?" It goes on to point out that sample weights, number of days, and the nutrient database do change over time, and so you have to take into account these effects. The above study covers effects as a result of changes in the nutrient database. I have trouble believing that sampling method or the data cycle length would result in such a major discontinuity in the data.
- crdb 11y ago
  So, I had a thought, and checked, and indeed, Dietary Fiber is 24-25g from 1998 onwards. Could it be as simple as someone accidentally including Dietary Fiber in Fats & Oils?

deleted 11y ago

[deleted]

zzalpha 11y ago

That's actually a very good observation! There does seem to be a major discontinuity between those two study periods. Very strange that it seems to only affect fats, and that the effect was so dramatic... They do mention "There has been some research that addressed the impact of changes in methods and/or databases between selected surveys"... it'd be worth digging that up to see what the effects were determined to be. Edit: Found it? http://naldc.nal.usda.gov/catalog/7349 http://naldc.nal.usda.gov/catalog/7349 Nothing in the abstract explains a major discontinuity in reported fat intake, though. They only report small but statistically significant effects on various other nutrients. Edit 2: They also have a FAQ on this topic. From http://www.ars.usda.gov/Services/docs.htm?docid=13793 http://www.ars.usda.gov/Services/docs.htm?docid=13793: "Is it possible to combine WWEIA data from different release cycles?" It goes on to point out that sample weights, number of days, and the nutrient database do change over time, and so you have to take into account these effects. The above study covers effects as a result of changes in the nutrient database. I have trouble believing that sampling method or the data cycle length would result in such a major discontinuity in the data.

crdb 11y ago
So, I had a thought, and checked, and indeed, Dietary Fiber is 24-25g from 1998 onwards. Could it be as simple as someone accidentally including Dietary Fiber in Fats & Oils?